1. Field of the Invention
The invention is directed to an electrochemical sensor having at least two electrodes communicating with a liquid measurement cell electrolyte within a housing enclosing the electrodes and the electrolyte. Electrochemical sensors are often used as gas detecting devices and as alarm devices. Solid electrolytes are frequently used as electrolytes (for example, see WO 91/16624). However, there are also a number of gas components which can only be measured by electrochemical sensors based on liquid and viscous-liquid measurement cell electrolytes.
2. Description of the Prior Art
In electrochemical sensors of the above-mentioned type, the electrolyte does not completely fill the interior of the sensor housing, since an easily compressible residual gas volume (air cushion) must remain in the measurement cell in order to compensate for alternating external pressures. Loss of electrolyte due to evaporation increases with the age of the measurement cell so that the residual gas volume in the sensor gradually increases with continued use of the sensor. In so doing, the residual gas volume is distributed to different locations in the measurement cell depending on the position or attitude of the sensor. For example, in a vertically upright sensor, a working electrode arranged at the top is completely separated from the electrolyte by the residual gas volume and the measurement cell no longer functions. For this reason, so-called electrolyte bridges, which form an electrical connection between the electrodes, are used in electrochemical sensors based on liquid electrolytes. Techniques for implementing such electrolyte bridges employ filter materials which have a sufficient capillary action to ensure the transport of electrolyte through the capillaries of the filter material. A problem is posed in that the electrolyte bridges must be mounted in the interior of the cell so that the majority of the electrolyte bridge is immersed in the electrolyte in every position of the measurement cell. Experience has shown that application of mechanical pressure against the electrolyte bridges to wet the electrodes is unsatisfactory and above all has poor reproducibility.